The White Rock Mesa Member of the Dakota Sandstone (Cretaceous) of the San Juan Basin, New Mexico and Colorado, a formal new lithostratigraphic unit to replace the informal "Dakota Main Body"

Abstract

—The White Rock Mesa Member of the Dakota Sandstone in the San Juan Basin of New Mexico and Colorado is formally named in this paper to replace the informal “Dakota main body” from a stratotype near Gallup, NM. It is an eastwardthinning clastic wedge of fluvial sandstone, carbonaceous shale, and coal that rests on the K-3 unconformity, which truncates lower Dakota members, the Burro Canyon Formation, and the Morrison Formation. A series of marine-flooding surfaces mark the top of the White Rock Mesa Member, and it grades into shoreface sandstones of the lower parasequence of the Cubero Sandstone Tongue of the Dakota to the east. It averages approximately 30 meters in thickness and is present in the western two thirds of the San Juan Basin. FIGURE 1. Topographic map of White Rock Mesa. Stratotype measured approximately along horizontal bar at west end of White Rock Mesa. USGS Church Rock 7.5’ Quadrangle.